The invention relates to a laser system with one or several actively controlled laser mirrors of the type which are actuated by electrostrictive materials, such as piezoelectric ceramics.
Known prior art laser systems of this type essentially are based on the employment of electrostrictive materials, such as piezoelectric ceramics for moving laser mirrors. However, such piezo actuators have considerable disadvantages, because the piezoelectric ceramics are not free of hysteresis, and furthermore usually require high voltage for triggering. In addition, the integration and processing of ceramic elements in the course of producing such laser systems is relatively expensive.
Essential manipulations in such devices are for example the tilting of the mirror or translation along its optical axis. 0n the one hand, the known systems require the integration of very different materials, so that monolithic production is not possible, and on the other hand piezoelectric ceramics have disadvantages in respect to their mechanical dimensions and the required high voltage. Added to this is the face that piezoelectric ceramics have resonance frequencies typically in the range of 100 KHz, so that the modulation of such ceramics beyond this frequency is possible not, at all, or is possible only with great difficulty. It should also be mentioned that in general self-destruction of the ceramic structure occurs with modulations in the range of the resonance frequency.
Usually, prior art laser mirrors have several dielectric coatings of different refractive indices in alternating sequence, which are applied to a glass substrate by vacuum evaporation. In this case, the thicknesses of the coatings have to be designed as a function of the wave length in such a way that the multi-beam reflection occurring at the boundary surfaces of the coatings leads to the desired degree of reflection by interference. This results in typical coating thicknesses of approximately one quarter of the light wave length (lambda/4) However, such a mirror with a glass substrate cannot easily be miniaturized and also has a relatively large passive mass, so that it cannot be moved very rapidly. Furthermore, such mirrors are relatively expensive, because for high optical quality the substrates must be individually polished, vacuum-evaporation coated and mounted or supported.
Modern lasers, however, are particularly distinguished by increasingly smaller dimension, along with pronounced high power density. Best known in this connection are the semiconductor lasers as well as solid body lasers pumped by semiconductor lasers. Mirrors with excellent optical properties and an exactly defined degree of reflection are required for operating such lasers. In most cases the mirrors are applied directly to the laser-active component in "monolithic" construction by means of a sequence of dielectric coatings. However, it is advantageous for a number of uses if at least one mirror is separated from the laser-active medium. On the one hand, in many cases this results in an improved beam quality and on the other hand it is possible to make the separate mirror to be movable or adjustable. With such an arrangement it is for example possible to perform a frequency modulation of the laser beam, or the laser can be turned on or off in case of slight tilting of the mirror which, when suitably controlled, results in the generation of so-called giant pulses (Q-mode) of very high peak output.
The requirements for compactness of laser mirrors continue to grow because of the increasing demands for further miniaturization. A diode-pumped, miniaturized compact body laser on an optical bank of silicon is disclosed, for example, in German patent document DE-PS 39 25 201, by means of which a compact micro-system can be realized.
It is an object of the present invention to provide a laser system of the type mentioned at the outset, which permits the rapid modulation of small laser mirrors, and whose mirrors are designed so as to permit economic mass production.
In a special embodiment, a miniaturized mirror is to be provided which has no other substrate materials except for the semiconductor substrate (silicon), can be micro-mechanically deflected in defined embodiments, can perform very rapid movements at high frequencies, and can be employed as an adaptive optical mirror system,
These and other objects and advantages are achieved according to the invention in which one or more micromechanically produced actively controlled laser mirrors are provided with an actuator which facilitates rapid manipulation thereof. The mirrors are produced by microelectronic fabrication techniques, and shaped from a semiconductor material which is embodied as an actuator mechanism. By means of optical coating techniques, a mirror is formed which can control the emission properties of a laser system,
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.